Take them to the range and let them hit a few balls. Then you can explain a few things to look out for. At first, they should just enjoy watching a ball fly.

Try to find a golf camp or clinic. It's a great way to introduce them to the game. They usually keep the focus on fun, while teaching them the basics. If their interest grows, then try to hook them up with a good instructor.
My personal experience is softball and golf don't mix well. My daughter was a tournament softball player for many years, and tried golf on and off but the different swing mechanics conflicted so she stopped golfing. At 20 she was done with softball, and started golfing again. Didn't take long to adjust her swing, and now she can outdrive me all day long. I still get her on the putting surface though. It was a long wait, but nothing beats being on the course with your kid playing golf. Greatest father-daughter sport in the world.

If they enjoy going to a range, if they want to get more, many courses offer summer camps for juniors. Basic courses, not like moving to FL for career development.

I'd see if there are any clinics or group lessons available. It's better for them to learn from someone who can teach them the basic fundamentals correctly before they get bad habits ingrained. These clinics should be keeping it fun for the girls and group them by age, sex or both. Plus, they will have access to clubs rather than hit your set which might be too long, too heavy, etc. for them.

and who knows? maybe they will come back and teach you a few things!

I would take them to the range to start and let them just swing away and try to give a few little pointers here and there. Give them fun little challenges "if you hit it close to that marker you win" etc. then start taking them to the course and letting them play when they wanted.

I second the above, a local clinic or camp is a great start. Definitely a different swing than softball so learning good fundamentals early is important. Another good thing if you have the room is chipping around the yard. Pretty easy to make a short course chipping to trees or putting a few stakes in the ground. Extra points if you have some slope so they can learn uphill and downhill lies.

Happy to hear! My son just started showing interest this summer. Great game to enjoy with the family.

find a golf clinic or school they can join. Up here in san diego on Sat afternoon there is a group kids clinic at Goat Hill which has a bunch of boys and girls and is great to meet and learn the game

Best advice my dad gave me at that age... just hit the ball as hard as you can. We did this at the driving range. The rest you can sort out later. Really alleviated any pressure to perform, and who doesn't love trying to bomb drivers :)

Theres been a clip making the rounds of social media the last few years of Padraig Harrington talking about this. Whatever you do, make it fun! Whatever they think is fun let them do it and then leave when its fun, dont let them get bored or start not enjoying the process. When its over, take them to have an ice cream or a soda, make it a memory for them. If you google it youll find his quotes!

Keep it fun. The quickest way to have them lose interest is making it seem like work.

I'll jump onto the clinic train here and add one more. Clinics and camps are great ways to introduce the basics, meet new friends with a shared interest, and receive instruction from someone other than you. As much as you know and as much as you love them, 99% of the time you're not the guy to frame swing changes to them because you're their dad. My course has a six session camp over two weeks that covers all the basics and culminates with a 9 hole family event - look around and I'm sure that you'll have one similar nearby.

Additionally, I've found that my kids respond best to taking them out for 9 holes with me. Usually it's just my 8 year old son, but half the time my 13 year old daughter will tag along and even less frequently my 16 year old son will come with too. Place them at an appropriate yardage; my two youngest get dropped off at 150-200 yards and my 16 year old plays the forward tees. When we're done we have a tradition of grabbing a Coke and a candy bar in the clubhouse and spend another 20-30 minutes talking or goofing off. Golf is really the byproduct of the true blessing - getting to spend those couple of hours with your kids!